The present invention relates generally to an annealing system for silicon thin films used with various semiconductor products such as ICs, TFTs, solar cells, and sensors, and more particularly to an annealing system and process that are capable of treating a silicon thin film formed on a glass substrate.
A conventional production process of semiconductor products makes use of an annealing step where impurities are doped on a given area on a substrate on which a silicon thin film such as polycrystalline silicon is laminated, and the impurities are then diffused or activated by heat treatment to form a source or drain, recover breaks in the crystals due to implantation of impurities, or crystallize an amorphous area, whereby various functions are made available.
When such annealing is carried out only by use of heat treatment with a heating device, no desired annealing effect is obtained at a heating temperature of lower than 1,000.degree. C. When a substrate formed of a material having relatively low heat resistance, e.g., glass is exposed to a high temperature exceeding 1,000.degree. C., the substrate is often disabled due to cracking or breaking. For an annealing step consisting only of heat treatment, therefore, it is required to use an expensive, difficult-to-handle, and heat-resistant material such as quartz for the substrate. This incurs a production cost rise, and places some limitation on the degree of freedom in processing equipment as well.
On the other hand, an annealing process making use of laser beam irradiation has been proposed or put to practical use as an alternative annealing means that does not rely upon a simple heat treatment. According to this process wherein a thin film on a substrate is directly irradiated with a laser beam, it is unnecessary to increase the temperature of the substrate to such a high temperature. However, when the laser beam irradiation process is used to increase the number of processing shots on a mass-production scale, it is required to increase the width of laser beams. As a result, there is a difference in the irradiation energy density between laser beams, which may otherwise make it difficult to achieve consistent annealing quality.